This invention relates to a thermoplastic resin composition having an excellent balance between impact resistance and heat resistance, and a process for preparing the same.
A polyphenylene ether (hereinafter referred to as "PPE") has been known as engineering plastics having excellent heat resistance, dimensional stability, nonhygroscopicity and electric characteristics, but it has drawbacks that melt fluidity (flowability when melting) is bad to make molding processing difficult, and also solvent resistance and impact resistance are poor.
On the other hand, a saturated polyester has been used widely as engineering plastics having excellent molding processability, solvent resistance and mechanical strength in the fields of parts for automobiles and parts for electric and electronic equipments. However, this resin has drawbacks that molding shrinkage rate and linear expansion coefficient are high, and also rigidity is greatly lowered at high temperature. In order to remove these drawbacks, there has been proposed a method of filling up a reinforcing agent such as glass fiber, but the method has a problem that appearance of a molded product is worsened so that application thereof is limited depending on the field.
If a composition having both good properties of PPE and the saturated polyester and compensating undesirable properties each other can be obtained, an excellent resin material having a wide application field can be provided, and it can be said that industrial significance of such a material is extremely great. Therefore, for the purpose of providing a molding material in which disadvantages of both resins are compensated each other without impairing advantages thereof, there have been disclosed, for example, compositions in which both resins are simply melted and mixed in Japanese Patent Publication No. 21664/1976 and Japanese Provisional Patent Publications No. 50050/1974, No. 75662/1974 and No. 159847/1984.
However, in such a simple blend system, PPE and the saturated polyester have inherently poor compatibility with each other so that adhesiveness at an interface of this two phase structure is not good, whereby two phases can hardly take uniform and fine forms. Therefore, when shear stress is applied to molding processing such as injection molding, laminar peeling (delamination) is easily caused, whereby appearance of a resulting molded product is worsened and an interface of two phases becomes a defective portion. Thus, it is impossible to obtain a composition having excellent mechanical characteristics such as dimensional stability, heat resistance and rigidity and excellent physical characteristics such as solvent resistance.
Therefore, there have been proposed several techniques of improving compatibility of both resins. There have been disclosed, for example, a method of using a modified PPE obtained by reacting a compound having both (i) a carbon-carbon double bond or a carbon-carbon triple bond and (ii) one or more selected from a carboxylic acid, an acid anhydride, an acid amide, an epoxy group and a hydroxyl group (Japanese Provisional Patent Publications No. 257958/1987 and No. 54427/1988 and PCT Provisional Patent Publication No. 500803/1988), a method of using an alkoxysilyl group-modified PPE (PCT Provisional Patent Publication No. 503392/1988), a method of using an oxazoline-modified PPE (Japanese Provisional Patent Publication No. 187453/1990), a method of using a polyester modified with a hydroxyl group- or carboxyl group-terminated polystyrene (Japanese Provisional Patent Publication No. 170852/1990), a method of formulating oxycarboxylic acids (Japanese Provisional Patent Publication No. 129259/1990) and a method of formulating a modified resin obtained by subjecting an epoxy compound to graft polymerization with a hydrogenated block copolymer comprising a vinyl aromatic polymer and a diene polymer (Japanese Provisional Patent Publication No. 128068/1988). However, even when these methods are used, compatibility of PPE and the saturated polyester cannot be improved sufficiently in many cases, and it cannot be said that mechanical characteristics of resulting compositions are sufficient. Thus, further improvement has been demanded.